Of increasing importance in the oil well drilling industry is the ability to drill longer and deeper wells at inclined angles, commonly called extended reach drilling (ERD). This technology is of great economic importance as current estimates are that 20% of the wells to be drilled in the year 2000 will be ERD wells. Currently, the majority of these wells are rotary drilled wells.
However, many technological problems are encountered in drilling long ERD well depths. One of the greatest current limitations is to overcome the friction incurred by the drill string rotating and sliding on the casing or formation. Because of frictional losses along the drill string, the maximum drilling depth for an ERD well is frequently limited by the power of the top drive system to provide torque to the bit, or the resistance of the drill string to slide down the hole, both of which limit the weight on the bit and hence the penetration rate of the drill bit or the maximum well depth.
A second major limitation is the need to steer the tool in three dimensional space through the rock formations; however, use of the existing technology results in frequent xe2x80x9ctripsxe2x80x9d to the surface for changes in equipment or equipment failures. One common problem is the short life of a downhole motor with bent sub (used for changing drilling direction). The short life requires additional trip time because of downhole failures. Also with the use of downhole motors comes the relatively low allowable weight-on-bit, which limits the overall drilling penetration rate. Of particular financial importance is the need to xe2x80x9ctripxe2x80x9d to the surface to install or remove the motor. Another associated problem is the need for frequent trips when using existing three-dimensional steering tools that have short times between downhole failures, high costs, and poor reliability.
Recent developments with coiled tubing (CT) drilling have focused on the ability to drill longer and more deviated holes with coiled tubing, rather rotary drill pipe. At least one configuration of CT drilling assembly is believed to use a tractor and a 3-D steering device; however, the use of coiled tubing prevents the ability to rotate the drill string while drilling, thus increasing the potential for differential sticking. Rotary drilling circumvents this potential problem by allowing continuous rotation of the drill string; and as will be discussed below, an improved 3-D steering device that uses a deflected pipe approach potentially improves system reliability. The present invention also can avoid use of a downhole motor which is a necessary component of a coiled tubing drilling system.
In summary, with ERD rotary drilled wells of greater length comes the increasing need for the combination of controllable steering that is not interrupted by equipment change outs or failures and the need for controllable weight-on-bit on very long drill strings.
This invention provides a means to overcome the several existing difficulties and limitations with an efficient, reliable rotary long reach drilling assembly.
One objective of this invention is to combine various well drilling components into a novel drilling assembly that will allow greater rotary drilling depths and steering ability than current methods involving use of the individual elements. In terms of today""s drilling objectives, the aim is to facilitate drilling to depths of at least 10,000 meters (31,000 feet) to beyond 12,000-18,000 meters (50,000 feet).
One embodiment of the long reach drilling assembly comprises the following elements:
(1) Means for cutting rock (drill bit),
(2) Three-dimensional (3-D) steering tool (Interceptor)with controls and means for communicating with various types of telemetry, and
(3) Tractor with Weight-On-Bit (WOB) sensor.
In addition, the following components are optional to the system:
(4) Mud pulse telemetry sub,
(5) Differential pressure regulator sub,
(6) Measurement-While-Drilling (MWD) sub,
(7) Logging-While Drilling (LWD) sub,
(8) Composite pipe with integral electrical line telemetry, and
(9) Surface telemetry system.
The combination of a 3-D steering tool with a tractor and a weight-on-bit device facilitates drilling of longer extended reach (ER) wells. In long reach boreholes where sliding the drill string is limited, the present invention uses the tractor to put more weight-on-bit while continuing steering along the desired course.
Briefly, another embodiment of the invention comprises a long reach drilling assembly which delivers continuous torque from the surface to the drill bit via a rotary drill string. This embodiment comprises an elongated rotary drill pipe extending from the surface through the bore, a drill bit mounted at a forward end of the drill pipe for drilling the bore through the formation, and a 3-D steering tool secured to the drill pipe for making inclination angle adjustments and azimuth angle adjustments at the drill bit during steering. The 3-D steering tool includes an onboard telemetry section to receive inclination angle and azimuth angle commands together with actual inclination angle and azimuth angle feedback signals during steering for use in controlling steering of the drill bit along a desired course. The assembly also includes a drilling tractor secured to the drill pipe, the tractor comprising a body, and a gripper secured to the body, including a gripper portion having a first position which limits movement of the gripper portion relative to the inner surface of the bore and a second position in which the gripper portion permits relative movement between the gripper portion and the inner surface of the bore. The tractor also includes a propulsion assembly for selectively continuously pulling and thrusting the body with respect to the gripper portion in the first position, and an onboard controller for controlling thrust or pull or speed of the tractor in the bore. The tractor applies force to the drill bit for drilling the bore along the desired course the direction of which is controlled by the steering tool. Rotary torque for driving the drill bit is transmitted from the surface through the drill pipe and structural components of, the 3-D steering tool and the drilling tractor.
These and other aspects of the invention will be more fully understood by referring to the following detailed description and the accompanying drawings.